1. Field of the Invention
The present invention relates to variable ratio actuating assemblies for vehicles, such as brake pedal assemblies having a variable pedal ratio. Also, the present invention may relate to other types of levers wherein variable ratio is used.
2. Description of Related Art
Actuating assemblies for operating input elements of vehicles are well-known and include assemblies such as brake pedal assemblies and hand lever assemblies. For example, known brake pedal assemblies include a pedal arm having one end that is pivotally mounted to a mounting structure (e.g., a bracket) provided in the vehicle to enable pivotal movement of the pedal arm about an operating pivot axis. The pedal arm includes an input connector in the form of a booster pin. This booster pin operatively connects to a master cylinder or brake booster push rod that is configured to actuate the master cylinder of the vehicle brake system for purposes of selectively engaging or disengaging the vehicle's brakes. The booster pin is positioned between the operating pivot axis of the pedal arm and a pedal foot pad at an end of the pedal arm opposite the end of the operating pivot axis.
The feel and effectiveness of the braking action experienced by the operator can be varied by changing the geometric pedal ratio, which refers to the geometric relationship between the levers and pivot points that make up the brake pedal assembly. This geometric ratio is related to the pedal's force ratio FB/FA, where FA is the amount of force applied to the input portion (e.g., the pedal pad) and FB is the amount of force applied to the input element (e.g., the brake booster rod). The above-noted brake pedal assembly has a fixed or static relationship between levers. That is, the master cylinder push rod attachment point, i.e., the booster pin, and the operating pivot axis of the pedal arm do not move relative to one another during pedal travel. The geometric pedal ratio for a fixed relationship between levers is typically expressed as R=a/b, where a is the distance between the operating pivot axis and the actuation point on the pedal foot pad, and b is the distance between the operating pivot axis and the master cylinder push rod attachment point, i.e., the booster pin. The force ratio does not exactly follow the ratio a/b, as the angle between the pedal arm and the booster pin varies during pedal travel. However, the force ratio does follow the geometric ratio somewhat closely for most applications.
In general, for a given pedal arm travel at a given input force, pedal assemblies with higher geometric pedal ratios generate greater forces that are applied to the brake system. However, the higher pedal ratio results in a shorter travel of the master cylinder push rod. Additionally, the higher pedal ratio effects the “pedal feel” in the braking action to the user.
With the new lines of larger and heavier trucks and SUVs on the market, and the desire to utilize common components throughout the full range of vehicles (such as the pedal assemblies and the brake boosters), it is desirable to have a higher pedal ratio so that adequate force is applied to the brake system in the event of booster assist failure, i.e., power brake assist is no longer functional. Specifically, the Federal Motor Vehicle Safety Standard and Regulations (FMVSS) dictates that when there is a booster assist failure, the vehicle must be stoppable within a certain distance within a specific pedal load.
However, as noted above, increasing the pedal ratio to accommodate the FMVSS requirements can hurt “pedal feel,” which is the operator's perception of comfort or reasonable operation. Moreover, increasing the pedal ratio will mean less travel of the master cylinder push rod for a given amount of pedal movement. The shorter travel of the master cylinder push rod may result in the push rod not being fully stroked to “bottom out” the master cylinder.
Variable ratio brake pedal assemblies are known in the art. For example, see U.S. Patent Application Publication No. US 2003/0106392 and U.S. Pat. No. 4,615,235. However, these variable ratio brake pedal assemblies include complex linkage mechanisms.